In many automobile models a rear window wiper is attached to or through the rear window itself, rather than the door or panel below. In some models this allows the window with the wiper to move independently from the door or panel below and the window can be opened without opening the whole of the rear door. In general a window wiper assembly includes a blade mounted on the exterior of the window that clears the window, a motor located in the interior of the vehicle or in the vehicle panels that drives the wiper blade, and an arm or connector that connects the motor to the blade. The window includes a pre-drilled aperture and the connector or part of the connector is inserted through the aperture. A window wiper a grommet is installed in the window aperture, forms a seal around the connector and prevents liquids from entering the vehicle through the window aperture.
The grommet is formed from an elastic material that deforms to allow the grommet to be inserted into the aperture in the window then return to its unstressed shape to seat firmly within the aperture. The grommet has a channel around the circumference of the exterior of the grommet that holds grommet in position in the window aperture. The glass of the window fills the channel, with the walls of the channel holding the grommet seated in the aperture. Typically, the grommet includes a hole through the core of the grommet and the connector is inserted through the hole to connect the exterior wiper blade and the interior motor. Since vehicles windows are often curved, the grommet can be asymmetrical in shape to match the curve of the window.
Once the window wiper is installed, the grommet serves as a waterproof or water resistant barrier between the outside environment and the inside of the automobile. It also serves to hold the window wiper assembly firmly in place. Because of the curve in the window, the grommet is curved to fit firmly against the window. A misaligned grommet will not form a seal with the window. For at least these reasons, it is important that the grommet is properly aligned with the window when it is inserted into the window aperture.
In some instances, the grommet is pulled into place in the window solely by hand. In other instances an assembler uses a plunger tool, threaded through the grommet and the aperture. The assembling employee pulls the thread manually until the grommet is seated within the aperture. Both methods can be slow and result in inaccurate alignment of the grommet within the window.
In the assembly of automobile windows, many components need to be added to the window including stickers, heating coils, and window wipers. Often, many of the additional components are installed by a window assembly machine, which holds the windows and installs the various components. Currently, however, some components are added manually; for example, the windshield wiper assembly.